112 



A MANUAL OF PHYSIOLOGY 



different, a correction would have to be made. The method is not a 

 good one, for the reason, among others, that the long tube introduces 

 an extra resistance. 



2. Ludwig's Stromuhr. This instrument measures the quantity 



of blood which passes in a given time 

 through the vessel at the cross-section 

 where it is inserted. It consists of a 

 U -shaped tube, with the limbs widened 

 into bulbs, but narrow at the free ends, 

 which are connected with a metal disc. 

 By rotating the instrument, these 

 ends can be placed alternately in 

 communication with a cannula in the 

 central, and another in the peripheral 

 portion of a divided artery ; or they 

 can be placed so that none of the 

 blood passes through the bulbs, but 

 all goes by a short-cut. One limb of 

 the instrument is filled with oil, and 

 the other with defibrinated blood. 

 The limb containing the oil is first 

 put into communication with the 

 central end, and that containing the 

 blood with the peripheral end of the 

 artery. The blood from the artery 

 rushes in and displaces the oil into 

 the other limb, the defibrinated blood 

 passing on into the circulation. As 

 soon as the blood has reached a 

 certain height, indicated by a mark, 

 the instrument is reversed, and the 

 oil is again displaced into the limb it 

 originally occupied. This process is 

 repeated' again and again, the time 

 from beginning to end of an experi- 

 ment being carefully noted. The 

 number of times the blood has filled 

 a bulb in that period, the capacity of 

 the bulb and the cross-section of the 

 vessel being known, all the data 

 required for calculating the velocity 

 of the blood in the vessel have been 

 obtained. 



Suppose, for example, that the 

 capacity of the bulb up to the mark 

 is 5 c.c., and that it is filled twelve 

 times in a minute, the quantity 

 flowing through the cross-section of 

 the artery is i c.c., or 1,000 cub. mm. 

 per second. Let the diameter of the 

 vessel be 3 mm., then its sectional area 



FIG. 39, STROMUHR OF LUDWIG 



AND DOGIEL. 



A, B, glass bulbs ; a, a metal 

 disc, to which A and G are at- 

 tached, and which can be rotated 

 on the disc b ; E, F, cannulae 

 attached to 6, and connected with 

 the peripheral and central end ; 

 of a divided bloodvessel. At the 

 beginning of the experiment, A 

 and the junction between A and B 

 are filled with oil ; B is filled with 

 physiological S3lt solution or de- 

 fibrinated blood : a being turned 

 into the position sh_wn in the 

 figure, the blood passes through F 

 and D into A, and the oil is forced 

 into B. As soon as the blood has 

 reached the mark m, the disc a, 

 with the bulbs, is rapidly rotated, 

 so that C is now opposite F. The 

 blood now passes into B, and the 

 oil is again driven into A. When 

 the oil has re.ched D, reversal is 

 again made, and so on. 



IS 7TX 



C 3 ) 1 



3-14x9 



= 7'o6 sq. mm. 



~, , ., . 1000 



Ihe velocity is ^^=141 mm. 



per second. 



Various improvements in this method have been made, such as a 

 graphic registration of the reversals of the stromuhr. 



